This invention relates to an olefinic resin composition. More particularly, it relates to an olefinic resin composition whose molded articles such as an automobile part or the like can be coated without a primer or without a degreasing step in some cases to obtain a molded article having satisfactory coating film performance, and said resin composition is also excellent in heat fusibility to various resins and metals.
Recently, a polypropylene resin or a polymer blend consisting of a polypropylene resin and an olefinic polymer rubber has been widely used in automobile parts, electrical appliance parts and the like. A thermoplastic olefin elastomer of a cross-linked type which is different from a mere polymer blend has been more preferably used than a thermoplastic elastomer of a polymer blend type because the former exhibits higher fluidity and higher heat distortion resistance in the soft flexural modulus region.
Molded articles of these elastomers are often coated; however, these molded articles may be said to have no ability to be coated because the constituents thereof are nonpolar. Accordingly, in the coating of these molded articles, there have generally been adopted the steps of degreasing by washing with a solvent vapor such as trichloroethylene, kerosine, an alcohol or the like, etching, applying a primer, applying a coating material and then baking the coating material. However, since labor-saving in the coating steps and low cost are desired and in particular, from the viewpoint of recent environmental protection, there has strongly been desired development of materials which do not require washing with trichloroethylene vapor or do not require any primer similarly to engineering plastics.
Further, for the same reason as mentioned above, these molded articles are inferior in heat fusibility to other resins, metals and the like, and hence, there is a considerable restriction in adopting such a simple method as two-color molding method or the like, and an improvement in this respect has been strongly desired.
This invention aims at providing a resin composition, the molded article of which does not require any primer in its coating and does not require a degreasing step in some cases and which is excellent in heat fusibility to various resins, metals and the like.
Until now, various proposals and reports have been made as to a method for achieving the good bonding of a coating film to the molded article without a primer in coating process of the molded article, and some of them have been put in practice. They can be broadly classified into the following three methods:
(1) A method of efficiently adding a polar group to the surface of the molded article by a surface treatment, and the surface treatment includes flame treatment, corona discharge treatment, plasma irradiation, ultraviolet ray irradiation and the like. PA0 (2) A method of introducing a polar group into the polymer. PA0 (3) A method in which a supplementary effect is calculated
(i) Blending a polymer having a polar group such as EVA, polyamide or the like or forming a polymer alloy with said polymer. PA1 (ii) Blending a polymer modified with an unsaturated carboxylic acid or its derivative, for example, maleic anhydride-modified HDPE, maleic anhydride-modified EVA, maleic anhydride-modified EPR or the like. PA1 (iii) A method of graft-modifying the whole of the composition with an unsaturated carboxylic acid or its derivative in the presence of an organic peroxide, for example, maleic anhydride-modified PP/EPR, maleic anhydride-modified styrene-grafted PP or the like. PA1 (i) Blending a rubber, filler and the like to improve the etching effect or anchoring effect. PA1 (ii) Removing components which tend to bleed to the surface of the molded article and form a weak boundary layer (referred to hereinafter as WBL), such as oligomer of the polymer, additives, oils and the like.
However, the above methods have the following problems:
The method (1) is effective to enhance the productivity of coating and stabilize the quality of product and is used in practice. However, an equipment cost and a running cost are newly required for the improvement of equipment.
The method (2)(i) has such a problem that it is difficult for the polar group to be effectively present on the surface of the molded article and the surface polarity of the molded article is changed with the lapse of time owing to the environment to fail to impart the desired ability to be coated to the surface. Also, the method (2)(iii) has such a problem that the amount of the polar group introduced is restricted and the coating is not sufficiently conducted and that unreacted polar group-containing monomer remains in a large amount in the polymer to cause an odor and corrosion of molds.
The method (3) calculates only a supplementary effect for imparting an ability to be coated to the surface of the molded article and cannot act as a substitute for the primer.